From Halopedia, the Halo wiki
Mare Frigoris (Latin for Cold Sea, or Sea of Cold) is a mare on Luna, the natural satellite of Earth. The mare is located within the Procellarum basin and is north of Mare Imbrium, near Luna's northern pole. Mare Frigoris became home to a human ice farm. Mason Hundley's father was an excavator pilot for ice farming in the region, and Mason used to help with spotting and excavation runs at the mare, until his father's death.